The present invention relates to lawn mowers and in particular to height adjustment mechanisms for lawn mowers.
Household lawn mowers comprise a cutting deck upon which is mounted a motor. The motor can be driven either by an electric motor powered by either a main electricity supply or a battery or an internal combustion engine. The motor rotatingly drives a cutting blade mounted below the cutting deck about a substantially vertical axis, which cuts the grass beneath the deck as it rotates. The cutting deck is commonly mounted on wheels or rollers, either having a fixed direction of travel so that the lawn mower moves over the lawn in a forward and reverse direction or having a variable direction of travel, for example castor wheels, so that the lawn mower is highly maneuverable.
It is desirable to have the height of the cutting blade adjustable in relation to the surface of the lawn in order to cut the grass to differing heights. One common way of achieving this is by having the cutting deck of the lawn mower mounted on the wheels or rollers in such a manner that the height of the deck, and hence the height of the cutting blade is adjustable relative to the wheels.
Such mechanisms include mounting the wheel or roller assemblies on the ends of levers which are pivotally mounted onto the deck and are capable of being releasably locked into a plurality of angular positions. The height of the cutting deck in relation to the wheels or rollers is dependent upon the angle of pivot of the levers. An interconnecting bar or bars are often added between the levers to ensure that the height of the deck can be adjusted by a single operation and that the height adjustment of interconnected wheels is conducted in unison.
It is desirable to be able to lock the height of the deck above the ground whilst the mower is being used. This can be achieved by locking the interconnecting bar or bars to prevent relative movement between the bar and deck thus locking the height adjustment mechanism on the wheels and thus fixing the height.
GB 2,328,359A discloses one such locking mechanism.
One problem with the design of the locking mechanism disclosed in GB 2 328 35.9 is that once the locking mechanism is released to allow movement of the interconnecting bar, the locking mechanism becomes detached from the interconnecting bar which results in the operator having to directly support and manipulate the deck.
In a first aspect, the invention is a lawn mower including a deck, wheel assemblies and height adjustment mechanisms positioned intermediate the deck and wheel assemblies. The lawn mower also includes an interconnecting bar positioned between at least two of the height adjustment mechanisms, the interconnecting bar being connected to the height adjustment mechanisms to transfer the movement of one height adjustment mechanism to the other height adjustment mechanism so that the height adjustment mechanisms operate in unison. A rack is located on the interconnecting bar; a locking mechanism attached with the rack holds the interconnecting bar stationary relative to the deck, the locking mechanism includes a pinion rotatably mounted on the deck, the pinion meshing with the rack to releasably lock the locking mechanism in a plurality of positions.
The present invention has the advantage that the pinion remains meshed with the rack at all times. Thus the operator can adjust the height of the deck by controlling the rotational movement of the pinion, thus avoiding the need to support the deck directly. The design is also simple in construction thus reducing costs of production and is easy to operate.
Preferably the pinion is capable of axially sliding between a first position where it is prevented from rotation movement and a second position where it is capable of freely rotating whilst remaining meshed with the rack.
The pinion can be biased towards the first position. Preferably, a cam mechanism is used to axially slide the pinion between the first and second positions. The use of a cam makes the operation of the locking mechanism simpler.
One method of mounting the pinion is to mount it co-axially and rigidly on an axially slideable rod, A knob can be rigidly mounted on one end of the rod. The cam mechanism can act between the knob and the body of a mower. When a mower is mounted on castor wheels, the mower is able to move sideways as well as in the more conventional forwards and backwards direction of travel. If the knob is located on the side of the body of the mower and an operator uses it to move the pinion from its first position to its second position against the biasing force of a spring, the body of the mower may tend to follow the knob, thus preventing the pinion sliding from its first to its second position. Therefore the body of the mower may be required to be held stationary whilst the knob and hence pinion is axially slid from its first position to its second position. The use of a cam mechanism between the knob and the body provides a simple mechanism by which relative movement of the knob relative to the body to be achieved without exerting a force onto the body which results in its movement.
The knob may abut against part of the deck when the pinion is in the first position. The cam mechanism may comprise a cam pivotally mounted on the knob and which comprises a lever. The use of a lever can enable an operator to operate the cam mechanism using the lever. The lever may comprise a large grip area. The benefit gained by the lever having a large grip area is that it is easy to grasp and enables the operator to use the lever to rotate the knob without too much strain on the operator""s fingers. Furthermore, by using the lever to rotate the knob, it keeps the hands of the operator away from the body of the mower. When the pinion abuts against the deck, it may co-operate with the deck to prevent the pinion from rotating when the pinion is in the first position.
In one possible construction, the knob or the rod can comprise protrusions which engage with apertures formed in a part of the deck when the pinion is in the first position to prevent the pinion from rotating. Alternatively, the deck can comprise protrusions which engage with apertures formed in the knob when the pinion is in the first position to prevent the pinion from rotating. A person skilled in the art realises that the protrusions can be formed in a range of shapes so long as rotational movement of the pinion is prevented when the protrusions are engaged with the apertures.
The pinion can have a small diameter and the knob can have a large diameter in order to provide a mechanical advantage to ease the height adjustment operation. By designing the knob and pinion so that the diameter pinion is small in relation to the diameter of the knob, a large mechanical advantage can be achieved which allows the height of the mower to be easily adjusted unaided either by mechanical means or by the operator having to apply additional forces manually to the deck to assist in the height adjustment process.
Such mechanical means can comprise biasing means which interacts between the deck and the wheel assemblies to provide an upward biasing force on the deck which counters, at least in part, the downward force of the deck due to its weight.
The use of biasing means eases the adjustment operation, particular, if no mechanical advantage is provided by design. The biasing means counters the height of the mower and thereby reduces forces acting on the height adjustment mechanism and hence transferred to the knob.
In one particular construction, the strength of biasing force can be such that it overcomes the downward force of the deck due to its weight in order to bias the deck to its highest position.
The biasing means can comprise a spring which is connected between the interconnecting bar and the deck. This provides a simple design.
Alternatively, the biasing means can comprise a torsion spring which connects between the knob and the deck and which provides a rotational biasing force on the knob. This provides a compact construction.